This invention relates to outdoor lighting fixtures or luminaires which utilize solid-state circuitry in their ballasts and, more particularly, to an improved mounting arrangement for a solid-state luminaire ballast which enables the solid-state portion of the ballast to be easily replaced.
The use of high-pressure mercury-vapor discharge lamps has greatly expanded in the past decade or so. Other types of high-intensity discharge lamps have also come into widespread use and examples of these other lamp types are the so-called high-pressure mercury-metal halide lamps and high-pressure sodium-mercury lamps. All of these discharge devices are generically known in the art as high intensity discharge (HID) light sources or lamps. All of these HID lamps are similar in that they require some sort of current limiting device to provide a ballasting therefor since the arcs all operate with what is known as a negative volt-ampere characteristic. In other words, the arc is of such nature that the higher the current, the lower the electrical resistance offered, with the result that without a current limiting device of some sort in series with the lamp, it would rapidly self destruct. In addition, the starting voltage required normally substantially exceeds the operating voltage. Because of these requirements, many different so-called solid-state circuits have been devised for operating such HID lamps.
Some solid-state ballast circuits use no inductor ballasting whatsoever. Some of the more promising solid-state circuits for operating HID lamps, however, utilize a combination of solid-state control circuitry and an inductor ballast or current limiting device. Since the original ballasts for HID lamps were inductors, the newer types of ballasts which combine the inductor with the solid-state circuitry can be termed hybrids, i.e., they combine both solid-state circuitry and inductors. These hybrid ballasts have shown a high degree of promise as far as competing both commercially and performance-wise with the prior inductor-ballast circuits.
A typical hybrid type circuit for an HID lamp is disclosed in U.S. Pat. No. 3,590,316 dated June 29, 1971 wherein the inductor portion of the ballast is designated as L2 in FIG. 2A of the patent and the solid-state circuitry controls the wattage of the lamp so that it is always the same, even though the voltage drop across the lamp may vary. A starting circuit which can be used to initially start any of a plurality of different types of lamps, as used in the previous circuit, is described in U.S. Pat. No. 3,519,881, dated July 7, 1970. Another hybrid-type ballast circuit is shown in U.S. Pat. No. 3,486,070 dated Dec. 23, 1969, wherein the inductor ballast portion of the circuit is designated 14 in FIG. 1, and the described solid-state circuitry is used to control the power which the lamp consumes. Another different circuit is disclosed in U.S. Pat. No. 3,222,572, dated Dec. 7, 1965.
In all of these hybrid circuits, the lamps are normally designed to consume a substantial amount of power, with a representative lamp rating being 400 watts. This has necessitated a relatively massive inductor ballast, which is normally located within the housing of the light fixture or so-called luminaire. The solid-state control circuitry, however, can be made to be very compact and most of this circuitry can even be placed upon a small chip. Some of the solid-state elements, however, normally require some sort of heat sink. Because of its size and ruggedness, the inductor portion of the lamp ballast is normally not susceptible to failure. If failures in the hybrid ballast do occur, they are most apt to occur in the relatively fragile and relatively complicated solid-state circuitry.
A solid-state photocontrol device with a heat-dissipating housing is disclosed in U.S. Pat. No. 3,621,337 dated Nov. 16, 1971.